Foamed granular glass

ABSTRACT

The blown granular glass consists of fragments of a blown glass element and comprises at least 100,000, preferably 1,000,000, per cm 3  of bubbles approximately of the same size. It is obtained by grinding the race material into a flour; the flour is mixed into a hot gas by a blowing means; the mixture is blown into a flat base furnace in an amount of blown glass; this amount is cooled after blowing and directly after cooling it is crushed into a granulated material.

BACKGROUND OF THE INVENTION

Some processes are already known (cf. Swiss Patent Specifications Nos.426,601 and 473,741 and International Patent Application No.PCT/CH79/00128) for manufacturing foamed granular glass from pulverizedglass, with the addition of a blowing agent releasing gas at highertemperatures.

Thereby, for preparing foamed granular glass, it was necessary first togrind the raw material to a powder, to mix this powder with a blowingagent releasing gas in heat, and to form raw granules from the soobtained mixture. The raw granulated material so obtained was then,appropriately together with a parting agent, preheated and blown in afurnace or on a drying belt.

The foamed granulated glass manufactured in this manner had aninhomogeneous structure insofar as the size and the distribution of thecells were different in the surface area of each granule from those inits interior. This fact led to a decrease in compressive strength in thesurface area of each granule, and thereby to a decrease in the totalcompressive strength.

Furthermore, some processes were also described (cf. Luxemburgian PatentSpecification No. 79,661, German Published Patent Applications Nos.2,206,448 and 2,224,009) for manufacturing blocks or plates of foamedglass which, if desired, could be broken down to a granulate. Thesepublications, however, do not contain any indication with respect to thephysical or mechanical properties of the granulated material. However,it is clear to the person skilled in the art that by the describedprocesses only relatively coarsely porous products, having a low numberof cells and an ununiform size of cells, a relatively high specificweight and a low compressive strength may be obtained.

SUMMARY OF THE INVENTION

It is the object of the invention to create a foamed granular glasshaving an improved compressive strength while having the same or areduced specific weight, as well as to create a simple and inexpensiveprocess for manufacturing such foamed granular glass.

The foamed granular glass according to the invention is characterized inthat it consists of fragments of a foamed glass element and comprises atleast 100,000, appropriately at least 500,000, and preferably at least1,000,000 of cavities per cm³ of at least approximately the same size.

The grains may have seamed edges.

A further subject of the invention is a process for manufacturing thefoamed granular glass according to the invention, which is characterizedin that the raw materials are ground into a powder, that this powder ismixed with an organic and/or inorganic blowing agent releasing gas inheat, that the mixture is blown into a flat strand of foamed glass in aflat bed furnace, that this strand is cooled after blowing and is brokeninto a granulate immediately after cooling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Appropriately, the blowing agent is applied as homogeneous layer ontothe surface of the glass grain.

Appropriately, the mixture of powder and blowing agent is gentlypre-dried before blowing, so that the water chemically bound in theblowing agent is not driven off.

If cooling is effected violently, the foamed glass strand, due tointernal stress, disintegrates into a granulate practically by itself,otherwise disintegration is effected preferably by mechanical breaking.

Preferably, the foamed glass strand is produced on a circulating,endless, caterpillar-like carrier consisting of a steel band or ofindividual links which, in its upper trace, is surrounded by a flat bedfurnace.

The thickness of the layer of the glass strand to be blown isappropriately dimensioned in such a manner that, per unit of area, itsheat capacity is greater than that of the carrier. Cooling of the blownfoamed glass strand is appropriately effected by cooling the carrier.

The surface of the carrier is preferably provided with a layer ofalumina or of an iron-aluminum alloy.

When manufacturing foamed granular glass having seamed edges, theobtained granulate is mechanically worked in such a manner, e.g. in adevice working like a coating pan, that the edges are broken.

By the process according to the invention, an extremely fine-pored, verylight granulate is obtained which may in particular be used as anaggregate for lightweight concrete and a filler for plastics. Theprocess particularly allows the production of a foamed granular glasshaving, per cm³, up to 3,000,000 closed cavities and a compressivestrength of more than 130 kg/cm² at a specific weight of 0.25. Suchphysical properties are not obtainable for a granulate which wasgranulated in its raw state and blown afterwards.

EXAMPLE

First, a pasty blowing agent was produced by mixing

100 parts by weight of water

32 parts by weight of water glass (28° Be)

4 parts by weight of glycerol (unpurified), and

15 parts by weight of sodium bentonite (clearing bentonite).

The blowing agent so obtained was mixed with 500 parts by weight offinely ground glass powder. The mixture is dried at 120° to 180° C. andif necessary sieved by means of a screen having 0.3 mm mesh aperture.

The glass powder activated in this manner, either in this composition,or after dilution with up to five times its amount of glass powder, isshortly blown in a layer of 0.5 to 5 cm thickness at 780° C. in anendless band conveyer furnace. When leaving the furnace, the strand offoamed glass is chilled and crushed to the desired granule size.

If a coarse granulate is desired, a mechanical crushing may be omitted,provided that chilling is effected very briskly, e.g. by means of water.In this case, the strand of foamed glass disintegrates solely due tointernal stress. Thereby, the obtained granulate is finer withdecreasing thickness of the strand of foamed glass.

I claim:
 1. Foamed granular glass, characterized in that it consists offragments of a foamed glass element having at least 100,000 cavities percm³ of at least approximately the same size; it has a compressivestrength greater than 130 kg/cm² ; and it has a specific weight of about0.25.
 2. Foamed granular glass as claimed in claim 1, characterized inthat it comprises at least 500,000 cavities per cm³.
 3. Foamed granularglass as claimed in claim 2, characterized in that it comprises at least1,000,000 cavities per cm³.
 4. Foamed granular glass as claimed in anyof claims 1 to 3, characterized in that the grains of granulate haveseamed edges.